Wisconsin Kirtland's Warbler Update

July 3, 2014

Adams County Nesting Report

Female Kirtland’s warbler at the Adams County site. Photo Courtesy of Ashley Hannah

The 2014 Kirtland’s nesting season in Adams County is near completion. To date, seven pairs of warblers have made eight nesting attempts (one pair renested). Jon and Ashley, our two nest monitors, found a total of eight nests. The first nest was found on June 4. Out of these eight nests, three were successful, four failed, and one is still active. For the successful nests, Ashley and Jon confirmed at least four nestlings to fledge, in total, and this number is likely an underestimate. For the failed nests, two were confirmed as unsuccessful due to brown-headed cowbird parasitism. Brown-headed cowbirds did fledge from the nests and the adult Kirtland’s were observed feeding the young cowbirds. One nest failed due to unknown reasons, but it was likely depredated by a predator. This Kirtland’s pair renested and unfortunately, the renest had two Kirtland’s warbler eggs and two brown-headed cowbird eggs. All four eggs were depredated and a least chipmunk, a known nest predator, was observed in close proximity to the nest. The one remaining active nest was confirmed on June 30 when Ashley watched both adults bring food to the nest to feed nestlings. This nest has four nestlings. Jon and Ashley continue to watch the sites with fledglings and monitor the one active nest.

Statewide Surveys

The annual statewide surveys started on May 15 and ended June 15. During these surveys, eight volunteers searched for Kirtland’s in six northern counties. Only one warbler was confirmed outside of Adams County during these surveys. The Kirtland’s warbler was observed in Marinette County in May and is still at the site. Jon searched the site to look for signs of nesting and determined that there was no female at the site and nesting was not occurring. The full results from the statewide survey will be provided in the next update.

Ron Refsnider weighs a male Kirtland’s before color-banding it. This unbanded male was located in Bayfield County.

Photo Courtesy of Joel Trick.

Adult Banding

Three previously unbanded males were color-banded in June in two Wisconsin counties. On June 6, Ashley notified the banding crew that she had observed two newly arrived and unbanded male Kirtland’s at the Adams County site. The banding crew quickly mobilized and was able to color-band both of the males on June 10. Ron determined both males to be one year old based on their feather plumage characteristics. The banding crew then traveled north to Bayfield County to band a male that was found at one of the playback sites on June 9 (see Broadcast Experiment). This male was not detected during the statewide survey and likely showed up in response to the playback. All three of these late-appearing males were never observed with a female, and all three disappeared within a few days of being banded. It will be interesting to see if they are sighted elsewhere.

Five to six day old nestling Kirtland’s. This nestling was color-banded and returned safely to its nest. It fledged on June 30. Photo Courtesy of Joel Trick

Nestling Banding

On June 24, Joel Trick and Ron Refsnider (retired USFWS biologists) and Sarah Warner (USFWS) had a successful morning banding Kirtland’s nestlings. This was the first attempt to band nestlings at the Adams County site. With the help of Ashley and Jon to locate the nest, two nestlings were banded and estimated to be between six to seven days old. There were also three eggs in the nest that never hatched. On June 30, Jon reported that the two newly banded nestlings had fledged the nest and the adults were busy feeding them at the nest-site area. Jon will continue to monitor the fledglings’ success. If these nestlings return to the Adams County site next year, we will be able to identify them based on their color-bands. This information is important in documenting survival and nest-site fidelity.

Broadcast Experiment

Out of the three playback study sites (Bayfield, Vilas, and Marinette) one unbanded Kirtland’s warbler showed up at a Bayfield County site on June 9. This male was banded on June 10 and aged to be one year old. It was still present on June 11, but was not observed again this year. Nick Anich (WDNR) speculates that this male moved on likely because it did not find a female in the area and there were no other males at the site. Possibly the playback itself was good enough to induce him to stop, but not to keep him there long, Nick suggests. To date, this is the only Kirtland’s that has likely arrived in response to the playback experiment (see June 3 update for more details about this experiment). The playback experiment will run for two more weeks.

A male Kirtland’s feeds a fledgling brown-headed cowbird. The nest of this Kirtland’s was parasitized by a cowbird.

Photo courtesy of Ashley Hannah.

Cowbird Trapping

We have had a lower cowbird trapping success this year compared to past years for reasons unknown. Cowbird traps have been in operation at the Adams County site since May 1. As of June 22, USDA Wildlife Specialist, Barry Benson, reports that a total of 109 cowbirds have been captured, consisting of 99 males and 10 females. This compares to 210 captured over eight weeks of trapping in 2012, and 197 over the same period in 2013. Since the nesting season is near completion, the cowbird traps will be taken down within the next week.